Electrical condenser and method of making it



Dec; 13, 1927.

W. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF BAKING IT 4 Sheets-Sheet 1 Filed March 0. $921 Wm M Dec. 13, 1927.

' 1,652,212- W. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF MAKING IT Filed March so. 1921 4 Sheets-Sheet s Dec. 13, '1927. 1, 52,212

' W. H. PRIESS ELECTRICAL CONDENSER AND METHOD OF MAKING IT Filed March 30. 1921 4 Sheets-Sheet 4 [if/WW 27 868..

Patented 1 Dev; 13, 1927.

UNITED STATES WILLIAM rnrnss, OE BELMONT, MAssAcnusET'rs; Assmnon TO WIRELESS swam. Y

f PATENT OFFICE.

unnnn'rus cOmrAnY, on BOSTON, MASSACHUSETTS, A CORPORATION OF NEW Your:

ELECTRICAL connnnsna snn METHOD E MAKING. 1'1.

Application filed March 30,1921. Serial N0.-456,903.

This inventionrelates to electrical con.- g densers and methods of making them. The invention is applicable to condensers of many types, for adaptation to high potential use, and specifically includes condensers of the sheet type for use in radio communicapifin circuits, electric power circuits and the The principal object of the invention is to provide a condenser adapted mechanically and electrically to preserve during service thehigh' pressure initiated upon the condenser stack during the process of manufam ture and consequent greatest practicable l5 closeness of contact of surfaces of dielectric and conducting sheets, all under conditions of compactness and lightness; the construction being adapted for use not only in service but during the process of manufacturing the condenser stack itself.

The present application constitutes a continuation in part of my co-pending application, Serial No. 332,421, filed 22.0ct0ber, "1919,and of my co-pendingapplication for Patent 1,553,549 dated Sept. 15, 1925.-

The invention consists of the features described in detail hereafter and illustrated in the best formin the drawings of which Figures ,1, 1 2, 4 and 5 are to scale and Figs.

3c 3 and 6 are reduced. Y I

' Figure 1 is' a longitudinal section of the casing or box and its cover for the condenser stack which embeddedor cast in wax, or immersed in oil in the casing, the stack being shown in elevation, and the clamping meansin place around the stack. i Fig. 1 is a perspective view of the spring plate used in the condenser.

Fig. 2 is a transverse section of the casing and cover showing the stack and its clamping means in elevation.

Fig. 3 is a perspective showing, in reduced scale,.of the completed and enclosed condenser ready for service, the casing being oblong in correspondence with the like shape of the sheets of the condenser stack, the

length being indicated in Fig. 1 and the width in Fig. 2.'

Fig. 4 is a side elevation of an embodiment the view ofa'stacloclamping member alone,

being taken as in Fig. 1, but the construction being specifically different from the clamping construction of Fig. 1 in that the two clamping members of Fig. 1 are joined together in Fig, 4 by two (Fig. 5)" integrally cast webs E.

Fig.5 is a plan view of the form shown in Fig. 4:. J v L Fig. 6 is a view of the condenser stack with clamping means of Figs. 4 and 5, the whole inverted for compression in the common arbor press shown, as a part of the process 0t treating the condenser stack.

The clamping means of this invention has several functions, although simple in appearance; and it is used to participate in a very refined process of manufacture, in addition to being designed to remain permanently with" the condenser stack as a functional part of the condenser for service conditions The construction will be described first, that to be followed by the points "which are now considered to be the most important ones in connection with the construction of the condenserywith the method or process of treatment of the condenser stack as involved with the use of the apparatus in connection with the methodyand in connection therewith. the operation in service of the condenser and its clamping means.

The condenser stack is at K of Figs/1 and 2. The clamping means also shown in said figures comprises the parts which, with the stack,.-are permanently enibedded or immersed in the solidified paralfin wax or oil W indicated by broken lines within the easing 26, which is usually but not necessaril of metal. The clamping member is of meta and by reason ofvits design it permits maintenance of the required high mechanical .pressure on the stack under conditions of greatly reduced space, the clamping means eingvery small relative to the high duty performed by it. The cover-G (since it has no clamping function) may be of; insulating material such as bakelite, mica moulded compositions or t e like, secured to casing 26 by screws 0' (Fig. 3). When of insulating -material, the cover provides r'or bringing out a condenser terminal or terminals. The clamp is especially designed,

as to its mechanical and electrical features.

for use, with condenser stacks whi h themselves are designed and processed to be adapted for high potential service; for example, the series sectional condenser disclosed in Figs. 1 and 2 is adapted to stand a voltage of approximately 20,000 volts or more at radio frequencies; although, of course, modifications of the clamp shown in Figs. 1, 2, 4 and 5 may be made to suit it for condensers of various operating frequency, current, voltage, capacity and consequent physical size. In high potential condensers it is desirable that "the stack, both in process of manufacture and in service, be subjected to continuous high mechanical pressure which approximates a thousand limit of pressure initiated during the process of manufacture and maintained during service is that which will not cause such deformation of the soft foil as the undue spreading thereof.- Hence the pressures used are those which are the highest practicable to be used without injuring the condenser..

The object of such highest practicable mechanical compression during process and service is to eliminate and keep out of the interior of the stack all foreign materials (such as air, moisture and wax or oil filler) to the greatest possible extent, so that the stack will consist so far as possible of nothing but the mica dielectric and conducting sheets, the surfaces of which are in intimate'contact with one another to the greatest possible eXtent. In my above-mentioned co-pending application, Serial No. 332,421, filed 22 October, 1919, I have described the advantages and reasons for the intimate contact above referred to. By this means (other things remaining e ual), a condenser is constituted which Wlll ave a maximum di-electric strength and a'minimum effective series resistance which will best withstand without injury the high voltages and currents to which it is subjected in the class of service for which it is designed.

The clamping means about to be described is a solution for a high potential, high frequency, condenser having a means that will apply-a pressure suflicient to force the surfaces of the sheets of the stack into and maintain them in intimate contact/with one another, both during process and service conditions, producing a condenser having a minimum ofloss and also having a'minimum bulk.

In Figs. 1 and 2 ar'efshown duplicate U- shaped metal clamping members or yokes 81 not connected together save via the metal base plate 83 to which their free ends are secured by pressure-retaining screws 84 extending through base plate 83 into lugs or enlargements S on the lower endsof yokes 81 but it is preferable, as shown in Figs. 4 and 5, that said two yokes 81 be joined by some such means as webs E cast integrally with the yokes, to prevent displacement of the individual yokes relatively to each other at their upper ends, and provide a path of maximul'n thermo conductivity froin the stack to the casing, via the filler.

The stack K of desired construction and not necessarily as shown (Figs. 1 and 2 showing a series sectional arrangement long known as suitable for high potential ser- Vice) rests on metal base-plate 83 from which the lower end'of the stack may be separated andinsulated if desired by a sheet of mica'82 (thickness being shown exaggerated). Base-plate 8 3 rests in a recess It in the bottom of casing 26 which serves to hold the stack in central position in the casing, in co-operation with the upper parts of yokes 81 which may bulge as at B (Fig. 2) to fit in vertical grooves G in the upper portions of opposite interior walls'of the casing'and extending from the top of the casing downwardly, having a decreasing depth, and serving to guide the stack into recess R which receives base plate 83.

In the construction illustrated in Fig. 2, the vertical portions of the clamping members 81 are shown spaced from the adjacent sides of the stack, providing insulation clearances sufiicient to prevent brushing or discharges from the stack to the clamping members 81*, the clamping members 81 being at the potential of the lowermost section of the stack and the potential in the stack increasing from section to section towards the top. The casing 26 is of metal and constitutes (or may constitute) one terminal of the condenser, being electrically connected to the lowermost section and at.

the potential'of the clamping members 81*. It is preferable and possible to have the whereby the size of the condenser for given electrical clearances is a minimum. Owing to the reater difference of potential between tge upper portion of the stack and clamp, the clamp requires more clearance at I stack K from the pressure plate P resting casing 26 closely fit the clamping means lead 40 to an upper terminal,

on said insulation 82". (Sheet 82* is illustrated exaggerated in thickness.) The parts at this location are not. so clearly shown in Fig. 2, being obscured by the copper strip Fi 2 being taken from the left of Fig. 1 where strip lead 40 extends upwardly from the upper:

most section of the condenser, its upper end.

being free and flexible and soldered and riveted to screw 28 passing through nut 30 (a rubber washer not shown) and insulating cover C to external threaded sleeve 29 in which is screwed the terminal binding screw 28*. The parts 30, 28 and 29 are held together andto the cover. C, and constitute the other terminal of the condenser (the high-potential t'erminal). A copper strip lead 40 is electrically connected to the lowermost section of stack K, which might be connected to the-outside in any desired way;

ing yokes 81 is uniformly distributed over the entire area of the mica and foil sheetsse,

.On top of pressure plate P is a spring which in the present embodiment of the in vention. is a metal springfplate 83 which,

when not under stress due to the high service pressure, is substantially. curved as 'shown in Fig. 1 This spring plate 83 is preferably made of special high grade material such as vanadium steel, clamping 10 yokes 81 being preferably of first steel.

In addition to' all the pregautions taken,

to make this clamping mean perfect both electrically and mechanically, the surfaces of the steel yokes 81*, base 83 and the pressure.

plate Pare copper-plated in order to reduce electrical losses by eddy currents, hysteresis I and the like.

By the clamping meansdisclosed, approximately a ton load is permitted on the stack.

' The spring pressure to be more fully described is permitted by the spring plate 83 to work over change of stack length in service of about one-eighth inch,. service changes of length being only of the magnitude of a few thousandths of an inch.

In constructing the spring plates 83", they are designed to require a pressure of approximately 1,000 lbs. per square inch of active stack area to flatten them out, and hence in constructing a condenser, the condition of the spring while under pressure is an index is preferably at least of of the pressure vapplied'and the builder will know that-sufiicient pressure has been applied when the spring is flattened.

For the purpose of transmitting the high pressure suitably to pressure-plate P, via floating spring-plate 83. which is separate from clamping members 81", the clamping yokes 8 l via upper spaced U ends 81 or D (Figs. 4 and 5) are provided in duplicate, one at each end of the spring plate 83 but in order to provide ample insulation between the metal parts, the clamping members 81 being atthe potential of the lower end of the stack and the spring plate 83 being at the potential of the upper endof the stack, a pair of spaced insulating members 82, preterably of mica sheets or other insulating material, are interposed between the ends of spring plate 83 and'the upper or U-ends 81 of yokes 81", the pressure being transmitted from said clamping yokes 8l" to pressureplate via these 'insulating members 82, under compression, and the spring plate .83 by compression of the same by the yokes 81 The insulators 82 are preferably constructed as shown toprovide a long leakage path between the metal parts at a difierence p of potential. By providing the spaced cross parts 81 of they clampingf member's 81 and the spaced insulators 82, sufficient space is .provided between them for locating the lower end of te'rmi'nal screw 28 above the stack, and at the same time insulating the screw from the members 81. The lead 40 is passed between one of the insulators 82 and the top ofthe stack and connected to the sc'rew28, insulating it from the clamp. The above construction provides a minimum of height for the condenser for given electrical clearancesj The above is the preferred specific arrangement for a stack as disclosed which has its opposite ends of opposite polarity,

all so that the upper electrical end of the stack (which may be the high potential end) -may be adequately insulated from the metal clamping yokes 81 and the base plate of the clamping means, which are in electrical connection with the lower electrical end of the stack. In practice, the upper end of the stack is usually the high potential end, the casing whenof metal as shown constituting the low potential terminal.

The insulating arrangements above described are ample for instances when there are differences of many thousands of volts between the two ends ofthe stack.

The lower or free ends of the clamping yokes .181 are connected to the clamping late 83, i. e., the base member of the clamps, by screws 84. In a construction involving a light mechanical system, the stated high mechanical pressure cannot be attained initially by these screws, if the screws are de signed solely for retaining tension loads,for turning them in an attempt to obtain such pressures would be liable to-introduce torsion strams that might twist off the screws or result in stripping the threads. The process to be described provides a means for small bulk of insulating material is required for mechanical and electrical reasons and almost any solid insulating material of low electric loss such as crystal quartz or the stack of mica sheets 82, Will be suitable to transmit by compression the pressure of the strong clamping yokes 81 to the stack K The employment of spring-plate 83, in addition to pressure-plate P, although not absolutely necessary in all cases, is usually preferred as being superior to non-elastic clamping means which is liable to receive a set upon the cooling and contraction of the stack after. heating and expansion under service conditions, so that a release of pressure on the stack would result. The more refined and painstaking the process of treat- "ment of the stack, pursuant to the process now to be described, the less variation there will be in the length of the'stack in service.

Following is a description of the method or process, illustrating how the clamping means and the casing 26 participate in the process in addition to remaining with the stack as permanent parts of the completed condenser, and maintaining permanently and preferably resiliently the high pressure initiated during the processing.

Prior to. the process, the lead foil sheets are rolled perfectly flat, and the mica sheets are measured for thickness, electrically tested, thoroughly dried, and placed for storage in air-tight containers.

My process is an improvement upon those claimed in the applications of Pickard,'S. N.

380,919, filed 12 May 1920, and Macpherson,

S. N. 384,501, filed 26 May 1920; and to the degree that my process is similar to those I may employ in the execution of my process, the apparatus disclosed in said applications and in the manner therein described.

First. Each sheet of mica and foil is separately coated with hot fluid or semi fluid insulating material such as molten paraflin, this wax being intended only as a temporary coating and serving as a detergent or agent for washing out air and moisture from between the stack-sheets. Preferably each sheet is coated ust before,it is put in place on top of another sheet in the building process. This coating preferably is effected by di pping the sheet in a bath of warm molten paraffin. (But my improvements in process ing may be applied to a stack built up of dry [non-waxed] sheets.)v

Second. A stack of such coated sheets is built up of alternate sheets of dielectric such as mica and foil (the wax-coatings being preferably warm and fluid as they are put in place and throughout the stack-building operation), and section separators or markers (temporary metal plates if so desired are at this time interposed between the stac sections to serve as markers for the purpose hereinafter described. In this buildin operation, additional sheets of mica and oil are used preferably for each section above the number calculated to be proper for a given desired cap'acit for a run of the thickest mica, so that ater on, after capacity test, sheets of mica and foil can be removed if the capacity he too high.

Third. A stack built as above is thoroughly heated by immersion in a bath of fluid insulating material such as the molten paraffin, until the insulating coating is so fluid that it can be the more readily squeezed out later, and after remaining lon enough in the bath to remove the moisture rom the stack; then the latter is removed and cooled under the highest practicable pressure, the pressure being applied during the bath, or just after the bath while the stack is hot,-all for the purpose of squeezing outthe paraflin, contained air, etc. This pressure at this stage can be applied either by way of any suitable temporary clamp such as a powerful C clamp or an arbor press as in Fig. 6, directly app1ied, the compression means being tightened as the stack cools to maintain the pressure. The heating of the stack of such sections as described (when the stack is'sectionalized) in the parafiin bath, is preferable, although each section could be thus heated separately. The heating of an entire stack of such sections reduces the necessary number of compression clamps, and the heating of the stack of sections is simpler and easier.

Fourth. The material stack after cooling is now split up, where the temporar separators are inserted, into sections to e used in making a series section condenser stack or to make condenser stacks of other types. The capacity of each section is now measured, and if too high as shown by measurement, surplus mica and foil sheets are removed, as proposed above under second to bring the section to the right capacity. Each section is also tested for voltage breakdown.

In case of a breakdown of any of the sections, each bad sectionis split into halves and each half tested to determine ,which is good. The bad half is then split into quarters and each quarter tested for the same purpose. The good halves are assembled to form a good section and likewise the good quarters, eighths, etc. The method above described 15 a very economical way of salvaging brokendown sections.

Fifth. When it is desired to make a final condenser stack, the good sections are then assembled, preferably with insulating separators 2 as shown in Fig. 1, consisting of mica sheets when thestack is a series see.- tional one, and the terminals of the sections soldered together as shown. v

Sixth. The assembled stack; is then put (when cold, i, e., without pie-heating as a direct preliminary to this step) in an arbor press (like that of Fig. (3 which is employed in the process). (If the condenser is not a sectional condenser, the above steps in so far as they pertain to treatment of sectional condensers may be omitted.) The pressure of the arbor press is then applied to the stack,

in the drawings, the clamp being applied at -this time either very tightly or under'only small pressure, this application of the clamp being when the stack is cold. At this stage, when the stack is cold (i. e., before being 'subj ected to thenext heating operation), the

stack is' put under the high compression .which was applied toit when or just after it was subjected to the above paraifin heating bath (third supra), this compression being appliedby the arbor press (Fig. 6) to the stack through the clamp, the screws 84L being tightened up for the purpose of retaining this pressure before removal of the stack from the press. 'As shown in Fig.

'6, the clamped condenser is inverted, basewith "paraffin; and the temporarily-filled casing may be further heated by applyingthe flame I of a Bunsen burner to the-exterior of theplate 83. being on top, thereby exposing screws 83 to convenient access for tighten ing while the condenser is held under compression in the jaws'of the ress. The foot-' rule U shows the actual dimensions of all the apparatus.

Eighth. The stack with its clamp is then thoroughly heated by immersion in a bath of hot.paraflin or of other hotinsulating fluid and then re-transferred tothe arbor press while hot, where it is again subjected 83 to a to the highest practicable spring compression applied through the clamp parts (which is, so tar-as is necessary, the final compressing operation); and if this results in any decrease in length (as from any furthersqueezing out of hot-paraffin, etc), the 84 are further tightened up While the stack yet under the heavy compres- (Usually this operation is performed by setting up the spring plate final given deflection. This spring plate is calculated and designed for a desired final pressure at a desired final deflection. Final condenser pressures are" thereby rendered "inherent with final deflection and are therefore rendered independent of an operators judgment.) This compression may be while the stack is in the heating bath or just after it is taken out of the heating bath (as in third supra). [If the pressure is applied while in the bath (enough presses being available for this purpose), then the subsequent preheating step before embedment in the insulating filler W (Fig.1) in casing 26 is unnecessary (referred to in ninth infra) because in such( case the stack is not allowed time to be cooled by treatment in the arbor press during the period of timeint'ervenin'g between the paraffin bath and the embedding operation,in other words, the above parafiin bath preliminary to the above final compressing may thus itself be the heating bath just preliminary to the embedding] This final compression results in a final washing out of the interior of the hot stack, thereby producing a stack having its interior as nearly as possible absolutely free of paraflin'or other insulating material, air" and moisture, and the mica .and foil sheets in the closest and most intimatecontact possible. r

' Ninth. The completed stack with its spring clamp in permanentcondition is now placed in the permanent casing 26, thecas ing when of metal being thereby adapted to receive a fluid insulating filler such [as molten araflin and permanently retain therein t e filler when cooled against expansion by-heating during service. (As to centralizing, see description above-of casing. recessB, casmg-grooves G and clamp-bulges B). The stack and clamp,-'and also the easmg supia) by temporarily filling the casing fluid insulating material such as molten casing. Thereupon the pie-heating bath in. the casing is poured outof the casing from around the .hot highly-compressed stack.

are then pre-he'ated (see eighth loo Thereupon the hot. stack in casing 26 is subj'ected to vacuum, V the hot molten paraffin or other fluid filler for permanent embedding is poured in the casing around the condenser, after wh ch the vacuum is discontinued. -By fluid insulating material or fluid filler is meant any material which during the application of the rocess is fluid or 'semisfluid or plastic, whetiher' maintained in"'thatcondition by heat or not and irrespective of whether or not such material or. fill'er is solid or semi solid at ordinary temperatures.

Thereupon the stackwith its permanent-' 'ly-applied spring clamp is left in the permanent embedding filler in the permanent and during this condition 4 casing 26; and the e'mbedment is solidified in cases where the filler is solid at' ordinary temperatures. If desired, and preferably, the embedding filler is cooled and solidified in such wise as to cause it to be free from cracks or voids, i. e., to be holosteric, this being effected by the application of a temporary waxing head (preferably as shown in said application of Macpherson) to the top of the permanent casing immediately after the clamped stack is placed in the easing 26. Then when the fluid embedding filler W is poured into the casing, suflicrent is poured in to fill up the temporary'waxing head also, so that during the cooling and solidificationof the wax in the casing there is a head of wax in the waxing head on top of the wax W in the casing around the stack. Thereupon the wax in casing and head is cooled gradually as by the abstraction of heat from the lower part of such Wax, i. e., in the casing, and the supply of heat to the upper part of the body of wax, i. e., in the Waxing head, so that the formation of cracks and voids is obviated in the Wax in the easing and limited to the wax in the temporary waxing head When the wax has thus cooled so that all cracks or voids exist only in the head of wax, and not at all in the embedding Wax W in the casing, the temporary waxing head and the paraffin there in are removed, leavin the embedding wax W flush with the top 0 the casing (Fig. l) and thereupon the rubber gasket Y and the insulating cover C are put in place.

Referring to Fig. 1, it is to be noted that before the stack K is put in the casing 26, the screw 28 has its: lower end soldered and riveted to the free end of the broad copper strip lead 40. Also the nut 30 is moved on screw 28 to the level which will permit said.

nut to lie against the lower surface of cover C when finallythe latter is put down into place, when screw 28 passes through an unthreaded hole in the cover. A rubber washer (not shown) is placed on top of nut- 30 before cover C is applied over it. After cover 1C is applied, internally threaded sleeve 29 may be screwed down on screw 28; and finally binding screw 28 is screwed into sleeve 29.

Herein mica means mica or its substantlal equivalent;-and so with lead foil, as other preferably soft metal foils may be used; and so with arafiin, as other waxes, 011s or insulating c caning and filler agents may be employed.

Since I have succeeded in separating the electrical functions of the cover and its mechanical function with respect to the .maintenance of stack pressure, I may use for the cover, materials of very fine electrical properties irrespective of their mechanical strength. For example, a mica sheet or a mica sheet and mica insulator may be used and advantage obtained, especially at high potent al and high frequency alternating currents due to the relatively low dielectric loss of mica and its superior dielectric strength and surface creepage properties. A quartz sheet or a thin porcelain sheet might likewise be used as a cover material, inasmuch as they have no mechanical function other than that of simple cover for the support of the high tension terminal. These materials, especially if thin, would have a low dielectric loss and have very fine creepage values.

It is to be understood that the invention is not limited to the embodiments and features specifically shown and described herein, but that such embodiments and features are subject to changes and modifications without any departure from the spirit oi the invention.

1. In an electrical condenser, a stack ol dielectric and conducting sheets; clamping means comprising a U-shaped yoke extend ing from one end of the stack to the other; and means connected thereto to maintain tht successive sheets of the stack inintimate contact, and a casing surrounding the clamped stack, said casing being provided witl grooves in itstinterior opposite walls arranged to receive and guide the sides of saic clamping yoke. I

In an electrical condenser,a stack 0' dielectric and conducting sheets; clamping means comprising a U-shaped yoke extend ing from one end of the stack to the other and means connected thereto to maintaii pressure on the stack, a casing open at on end toreceive the clamped stack and being formed upon opposite inner sides Witl grooves in which lateral upper portions 0 said yoke enter as the clamped stack is in troduced into the casing; and means at th bottom of the casing to receive the botton of the clamped stack and to co-operate Wit] said grooves'to center the clamped stac. within the casing.

3. In an electrical condenser of the series section sheet type, the improvement in mean for holding the stack under high compres sion, which comprises two metal vparts, on of which is a base-plate for engagemen with one end of the stack of sheets, and th other of which is a U-shaped member havin wide opposite sides for facing opposite side of the stack, the inner walls of said wid sides having inclined surfaces roviding f0 wider spacing from the higlier potentiz portion of the two sides of the stack whici it faces, said U-shaped member at its intei mediate portion adjacent t-he other end 0 the condenser from the base-plate bein formed in two portions separated from on another for clamping that end of the stack and means for securing together the has plate and U-shaped member.

t. An electrical condenser which con prises a stack of dielectric and conducting sheets compressed together to be held in intimate contact with one another, and clamp-- ing means constructed to maintain such compression and including parts consistin of a metal such as steel having high speci 0 resistance and magnetic "permeability, said metal parts being provided with a coating of copper to reduce losses from eddy cur-. rents. p e

5. In an electrical condenser, a stack of sectionsconnected in series and comprising alternate sheets of foil and dielectric, the opposite ends of the stack being at a difference of potential, a metal clamping memher for said stack and permissively at the potential of one end thereof and insulated from the opposite end thereof and spaced from the lateral portions of the stack to provide insulation clearance, a metal casing surrounding said stack and clamping member, permissively at the potential of the clamping member, and provided with grooves upon its inner surfaces adjacent to the lateral portions of the clamping mem- ,ber into which grooves the cl'amping member fits.

6. In an electrical condenser, a stack of dielectric and conducting sheets divided into series-connected sections and having high potential difierenc'e across its ends; an allmetal clamping means extending from end to end of the stack and tending to pull said ends together, said clamping means ,being permissively at the potential of the lower end of the stack and insulated from the oppositeend and sides thereof; a metal casing enclosing the clamped stack and on the bottom of which it is supported; said casing engaging said clamping means at the sides and bottom and permissively at ,the potential of the clamping means; a cover of insulating material for said casing, the clamping means being functionally independent of the casing and cover; a condenser terminal located above the stack and mounted in the casing-. cover; and a conducting'lead extending from the uppermost section of the stack to said terminal.

7 In an electrical condenser, a stack of sections connected in series and having its opposite ends at a difference of potential, a base plate on which the stack rests, U-shaped metal clamping means secured at its ends to said base plate and extending across the opposite end of the stack in two spaced. parts atopposite sides of said opposite end, spaced, insulating members interposed between'the said opposite end of the stack and the crossing parts of said clamping means, said clamping means and base plate bein permissively at the potential of the lowe iend of the stack, a metal casing. re-

ceiving said stack and clamp and being at.

the opposite end of the stack, insulating,

membersupon the pressure plate at opposite sides thereof and spaced from each otherand a metal clamping member connected to said'base plate and extending along opposite sides of the stack and havingtwo spaced parts extending over said insulating mem hers whereby the sheets of the stack are maintained inintimate contact, said 'clamp-. ing member being permissively at the potential of the lower end of the stack, a metal casing enclosing said stack and clamping meansand permissively at the potential of the lower end of the stack, a cover of insulating material; a terminal located in said cover over the end of the stack and between said insulating members, a conductinglead from an adjacent end section extending between the end of the stack and one of saidinsulating members and connected to said terminal, and an insulating filler in said-casing surrounding the stack,

9. In an electrical condenser'of the type comprising a stack of conducting and dielectrio sheets electrically divided into seriesconnected sections whereby in service a high difference of potential may be applied across the. two ends of the stack, the combination sion by the clamping means, and acting to prevent the stack from being short-circuited by' the metal of, the clamping means.

10. In an electrical condenser of the type comprising astack of dielectric and conducting sheets in -intimate contact with one another; rigid all-metal clamping means for maintaining such intimate contact and extending from one end of the stack to the other and constructed ,to tend to pull the ends of the stack together; and a spring interposed between one'end of the stack and the corresponding end of said clamping means.

11. In an electrical condenser of the type comprising a stock of dielectric and conducting sheets in intimate contact w1th one an:

' to draw said plates toward one another: and

other, of means for maintaining such contact which includes metal plates facing and acting against the opposite ends of the stack, and rigid metallic means extending from end to end of the stack along opposite sides thereof andconstructed to tend a spring interposed between said metallic means and one of said metal plates; said metallic means acting through said spring and on the metal plate at the other end of the stack to hold the spring under strain and hold the metal plates in positions to maintain said intimate contact.

12. In an electrical condenser, a stack of sections connected inse'ries and comprising dielectric and conducting sheets; a pressure plate facing andv acting against one end of the stack; a spring plate facing and acting against said pressure plate; a casing enclosing said parts and including a cover; an allmetal clamp supported within and by said casing and functioning independently of the casing and cover. said clamp being constructed to extend from end to end of and exterior tothe stack and to act on said pressure plateand spring plate to tend to pull them toward the opposite end of the stack; and insulating material located between the all-metal clamp and one end of the stack, held under the compression of said clamp, and preventing short-circuiting the stack by said metal clamp. L

13. In an electrical condensen'a stack of sections connected in series and comprising alternate sheets of foil and dielectric, the opposite ends of the said stack being at a difference of potential, and clamping means for exerting pressure over opposite ends of the stack, and including insulation under compression insulating the opposite ends of the stack from each other, and including also a spring plate under stress whereby said pressure is maintained resiliently.

, 14. In an electrical condenser of the type comprising a stack of dielectric and conducting sheets, a metal "pressure plate facing and acting against one end of the stack; a metal spring plate facing and acting against said pressure late; and a metallic clamp extending rigid y alongside the stack and from end to end thereof and constructed to tend to pull said pressure plate and spring plate toward the opposite end of the stack. k 15. The herein-described method of male ing a sheet-stack of an electrical condenser, which consists in building up a stack of waxcoated sheets of dielectric and conducting material, highly compressing such stack at room temperature, maintaining such compression by tightening a permanent clamping'device .around the ends of the stack; heating the then highly compressed stack by a hot insulating fluid; further compressing the then hot stack to an extent greater creased compression by further tightening said clamping means.

16. An electrical condenser comprisin a stack of sheets constructed to have a difference of potential between its opposite ends; clamping means for the ends thereof consisting of a spring metal clamping plate extending over one end of the stack; a metallic' clamping yoke looped over the stack end; metallic ad uSti-ng means co-operating with said yoke to flex the spring metal clamping -plate; and insulating material held under compression between one end of the stack and said clamping means.

17. {The herein-described method of making condensers which consists in building a stack of sheets of foil and dielectric, treating said stack to a bath of hot insulating fluid, applying permanent high spring pressure to said stack to squeeze out the insulating fluid and bring the sheets into intimate contact, subjecting said stack while under said spring pressure toa bath of hot insulating fluid, and then permanently surrounding said stack with an insulating fluid while under said spring pressure, substantially as described.

18. The herein-described method of mak-, ing condensers which consists in building -a stack of: sheets of foil and dielectric, treating said stack to a bath of hot insulating fluid, applying permanent high spring pressure to said stack to squeeze out the fluid and bring the "sheets into intimate contact, temporarily heating said stack with hot insulating fluid while maintaining said spring pressure, applying vacuum to the stack while hot and under said spring pressure and then permanently surrounding the warm stack while under said pressure and vacuum with an insulating fluid, substantially as described.

19. The herein-described method of maliing a condenser which .consists in building a material stack of, alternate sheets of foil and dielectric andapplying hot fluid insulating material, squeezing out the air and moisture with the insulating material by the application of high pressure, cooling said material stack while under pressure, separating the material stack into sections and connecting such sections together to form a condenser stack, again treating the sectional stack with hot fluid insulating material and applying permanent high spring pressure to bring the shets into permanent intimate contact, heating the stack while under the spring pressure by atemporary wash of hot fluid insulating material, applying a vacuum while the stack is hot and under said spring pressure, and finally surrounding the ill) 20." The herein-described method of building a condenser, whichconsists in separately coating sheets of dielectric with insulating "material and'building a material stack of alternate sheets of foil and such coated sheets, washing out air and moisture from the inside of the material stack by heating the stack and squeezing out the insulating material by pressure, then allowing the material stack to cool while under pressure; separating the material stack into sections, assembling a number of sections into a con- "denser stack and connecting the sections and inserting insulating sheets between them; reheating the stack in a bath of insulating material and a applying spring pressure of the order of a thousand pounds per square inch to the stack; preheating the stack while maintaining the spring pressure ofthe order specifiedi'by temporarily washing the stack with hot insulating fluid; subjecting the hot stack while under the spring pressure of the order specified to a vacuum and while in vacuum surrounding the stack with fluid in sulating material, and solidifying the embedding insulating material by gradually cooling from the bottom upwardly, the spring compression being maintained on the condenser throughout cooling and in service substantially as described.

21. The herein-described method of build,-

iilg a condenser, which consists in coating sheets of dielectric with an insulating fluid, then building a material stack of the temporarily-coated sheets and foil, washing out the air and moisture from the inside of the material stack by heating the stack and applying pressure squeezing outthe insulating fluid with the air and moisture, and then cooling the stack while under high mechanical compression; separating the material stack into sections, adjusting the capacity of each section, and testing for breakdown; assembling a number of sections to make a condenser by connecting them; measuringthe stack capacity under compression and correcting it, if necessary; applying permanent spring pressure of the order of a thousand pounds per square inch to the stack tomaintain the sheets in intimate contact; heating the stack in hot insulating fluid while the spring pressure is being applied; preheating the stack by means of a temporary wash of hot insulating fluid; sub-' jecting the stack to vacuum while maintaining the stack under the spring pressure of the order of magnitude specified; then while electric, applying permanent spring'pressure to said stack, temporarily heating said stack while under the spring pressure, subjectin said stack while hot and under the sai spring pressure to a vacuum, and finally surrounding said stack while under the spring pressure and vacuum with fluid insulating material.

'23. In an electrical condenser having a stack of dielectric and conducting sheets, a. clamp having a metal base-plate facing one end of the stack, and two U-shaped metal members comprising two spaced portions extending across the opposite end of the stack,

said. U-shaped members being joined 130-.

gether bywide sides consisting of integral webs adjoining opposite sides of the stack,- and the lower ends of said sides of theiU- shaped member being adjustably secured to said metal base-plate. u

24:. In an electrical condenser of the type having a stack of series-connected sections with high potential across its ends, the .com-- bination with a metal casing enclosing jsuch stack and a cover therefor, the Stack being arranged to have its low potential end near the bottom of the casing; a metal base-plate at the bottom'of the casing and supporting the stack; a metal U clamp secured at its lower and freeends to said metal-base plate and extending up over the sides of the stack and having two separated top portions ex tending over the to or high potential end of the stack; insulating material held under compression of the clamp between said two separated portions of the clamp and the stack; and a high potential connection extending from a top section of the stack to an open side of the U clamp, underthe in-' sulating material lying beneath one of said top portions of the clamp, and out be 0ndthe end of the stack from between sai separated portions of the clamp.

WILLIAM H. PRIESS. 

